The present invention relates to color video signal contour correction, and more particularly to such correction that is less for some colored areas, e.g., fleshtones, of the scene than for the remaining areas.
"Contours" is a term used in broadcast television camera system art to denote the signal that represents the changes between adjacent picture elements, both horizonta11y and vertically. The vertical contour signal is typically generated by averaging signals from points above and below the point in question and then subtracting the resulting average from the signal representing the point in question. Similarly, the horizontal contour signal is generated by averaging signals representing points to the left and right of the point in question and then subtracting the resulting average from the signal representing the point in question. It might be thought that a picture that is as sharp as possible would be desirable and thus a large amount of both horizontal and vertical contour should be added to the luminance signal representing the point in question. A circuit capable of doing this is shown in FIG. 1 where the amplitude of the combined horizontal and vertical contour signal received at terminal 11 is controlled by potentiometer 10 and the adding to the luminance signal received at terminal 13 is done by adder 12. However, a high amplitude contour signal is not necessarily desirable. Consider a "head-and-shoulders" shot of an aesthetically pleasing female. If the contour signal amplitude is large, every wrinkle and pore on the face will be so accentuated as to reduce her aesthetic qualities. Similarly, for a male face, unshaven facial hairs will be accentuated. Of course, hair on the head and the background, look pleasingly sharp. In this situation, the camera operator reduces the contour signal amplitude in order to make a trade-off between "sharp hair" and "unaesthetic face".
It is therefore desirable to have a contour correction system where the amount of contour correction varies with the color represented by said video signal.